Tregs are important to maintain CD4+ Tconv hypofunction in allograft tolerance.

Abstract

Abstract Regulatory T cells (Tregs) are necessary for the induction of murine cardiac transplantation tolerance via costimulation blockade. In this model, peri-transplant Treg depletion prevents induction of graft-reactive Tconv hypofunction. Whether Tregs are necessary to maintain Tconv dysfunction long-term after tolerance has been achieved remains to be seen. Our preliminary data indicate that complete depletion of Tregs using diphtheria toxin (DT) in Foxp3-DTR mice at the maintenance phase of tolerance precipitated rejection of previously tolerized cardiac allografts and resulted in the de novo production of graft-specific alloantibodies – potentially implying a reinvigoration of Tconvs which then provide help to B cells. Indeed, these Tconvs showed a trend toward renewed cytokine production after Treg depletion and were transcriptionally distinct by RNAseq from Tconvs in tolerant mice. Conversely, Tconvs from tolerant mice infected with Listeria monocytogenes, which precipitates rejection, were transcriptionally similar to Tconvs from unmanipulated tolerant mice. Gene set enrichment analysis revealed that B cell-mediated immune response related pathways were enriched in differentially expressed genes between graft-specific Tconvs from tolerant and Treg-depleted mice. Tconvs from Treg-depleted mice expressed significantly higher levels of genes associated with Tfh cell differentiation compared to both tolerant and naïve graft-reactive Tconvs. This indicates a unique state of potential reinvigoration and implicates Tregs in actively maintaining dysfunction of graft-specific Tconvs, and also suggests that hypofunctional graft-reactive Tconvs may become Tfh cells when reinvigorated by Treg depletion. Supported by the T32 Immunology Training Grant.